fix(i18n): add i18n support for custom model feature in ModelSelector (#172)

* feat(models): add custom model name input with provider selector

- Add custom model input field at bottom of model selector modal
- Add provider dropdown to specify target provider for custom model
- Track custom models in app store and display with CUSTOM badge
- Merge custom model into provider group list
- Fix custom provider models being overwritten by API response (keep both)

* Upload screenshot

* fix(i18n): add i18n support for custom model feature in ModelSelector

Replace hardcoded English strings (CUSTOM badge, placeholder, hint) with
vue-i18n t() calls and add corresponding translation keys to all 8 locales
(en, zh, ja, ko, fr, es, de, pt).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: toller892 <892@users.noreply.github.com>
Co-authored-by: Tony <125938283+toller892@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/client/src/i18n/locales/de.ts

@@ -252,6 +252,9 @@ export default {
     nousApproved: 'Login erfolgreich',
     nousDenied: 'Autorisierung wurde abgelehnt',
     nousExpired: 'Autorisierung abgelaufen',
+    customBadge: 'BENUTZERDEF.',
+    customModelPlaceholder: 'Benutzerdefinierter Modellname',
+    customModelHint: 'Enter zum Laden',
     noProviders: 'Keine Anbieter gefunden. Fugen Sie einen benutzerdefinierten Anbieter hinzu, um zu beginnen.',
     builtIn: 'Integriert',
     customType: 'Benutzerdefiniert',